Heat sinks with interdigitated heat pipes

ABSTRACT

A chip package includes adjacent integrated circuits on a circuit board, and separate heat sinks are thermally coupled to the integrated circuits. Because the integrated circuits are in close proximity, heat pipes in the separate heat sinks are interdigitated to prevent mechanical interference between the heat sinks. The amount of interdigitation depends on the separation between the integrated circuits and how the integrated circuits are arranged relative to an external fluid (such as flowing air). At the minimum, the heat pipes in fin regions of the heat sinks (which include fins for convective heat transfer to the external fluid) are interdigitated. However, the heat pipes may be interdigitated in pedestal regions of the heat sinks (which are thermally coupled to the integrated circuits) and/or in ramp regions of the heat sinks (in which vertical positions of the heat sinks change from the pedestal regions to the fin regions).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application Ser. No. 61/972,924, entitled “Heat Sinks WithInterdigitated Heat Pipes”, by Bruce M. Guenin and David W. Copeland,filed on Mar. 31, 2014. This application also claims priority under 35U.S.C. §119(e) to U.S. Provisional Application Ser. No. 61/863,057,entitled “Integrated Heat Pipe Heat Sink,” by Bruce M. Guenin and DavidW. Copeland, filed on Aug. 7, 2013, the contents of which are hereinincorporated by reference.

This application is related to U.S. Non-provisional patent applicationSer. No. 14/250,237, entitled “Winged Heat Sink,” by David C. Douglas,David W. Copeland and Bruce M. Guenin, filed on Apr. 10, 2014, thecontents of which are herein incorporated by reference.

BACKGROUND

1. Field

The present disclosure generally relates to a chip package forsemiconductor dies or chips. More specifically, the present disclosurerelates to a chip package that includes heat sinks with interdigitatedheat pipes.

2. Related Art

Many chip packages contain multiple integrated circuits. Duringoperation, these integrated circuits generate heat. This heat is oftenconducted away from the integrated circuits using thermal-managementtechniques, such as heat sinks with heat pipes having high thermalconductivity, which transport the heat to fins, which transport the heataway convectively via forced air.

The presence of multiple integrated circuits on a circuit board can posedesign and performance challenges. For example, if two adjacentintegrated circuits on a circuit board are separated by a smalldistance, a single heat sink may be used for both integrated circuits.This heat sink may be thermally coupled to the two integrated circuitsusing a thermal-interface material. However, if the top surfaces of thetwo integrated circuits are not coplanar, there can be significantvariations in the thickness of the thermal-interface material, which canreduce the thermal performance of the heat sinks.

Furthermore, if separate heat sinks are used for each of the integratedcircuits and the adjacent integrated circuits are separated by a smalldistance, the fins of the two heat sinks may mechanically interfere witheach other. This problem can be addressed by truncating the fins and/orthe length of the heat pipes at regions of mechanical interference.However, this truncation can reduce the thermal performance of the heatsinks.

Hence, what is needed is a chip package without the above-describedproblems.

SUMMARY

One embodiment of the present disclosure provides a chip package thatincludes: a circuit board; a first integrated circuit and secondintegrated circuit disposed on the circuit board, where the firstintegrated circuit is adjacent to the second integrated circuit; a firstheat sink having heat pipes that conduct heat away from the firstintegrated circuit; and a second heat sink having heat pipes thatconduct heat away from the second integrated circuit. Moreover, a givenheat sink for a given integrated circuit includes: a pedestal regionmechanically coupled to the given integrated circuit; a ramp region thatextends a vertical position of a portion of the given heat sink; and afin region having fins that convectively transfer the heat to anexternal fluid. Furthermore, the heat pipes in the fin region of thefirst heat sink are interdigitated with the heat pipes in the fin regionof the second heat sink.

Note that the fins in the fin region of the first heat sink and the finsin the fin region of the second heat sink may be: aligned, staggeredand/or overlapped.

In some embodiments, the external fluid has a flow direction, and thefirst integrated circuit and the second integrated circuit are arrangedalong the flow direction. Moreover, the chip package may include a lidand/or a given pedestal in the pedestal region of the given heat sink.

Alternatively, in some embodiments the first integrated circuit and thesecond integrated circuit are arranged perpendicular to the flowdirection, and the heat pipes in at least a portion of the ramp regionof the first heat sink may be interdigitated with the heat pipes in atleast a portion of the ramp region of the second heat sink. Furthermore,the heat pipes in at least a portion of the pedestal region of the firstheat sink may be interdigitated with the heat pipes in at least aportion of the pedestal region of the second heat sink. In theseembodiments, the heat pipes in the pedestal region of the first heatsink may be aligned with the heat pipes in the pedestal region of thesecond heat sink and/or the heat pipes in the pedestal region of thefirst heat sink may be staggered between the heat pipes in the pedestalregion of the second heat sink.

Note that a cross-section of the heat pipes in the pedestal region ofthe first heat sink and a cross-section of the heat pipes in thepedestal region of the second heat sink may be modified atinterdigitated locations.

In some embodiments, the chip package includes a lid and/or a givenpedestal in the pedestal region of the given heat sink.

Moreover, a width of at least a subset of the heat pipes of the givenheat sink may be varied over lengths of at least the subset of the heatpipes. Furthermore, a thickness of the given pedestal may be varied overa width of the given pedestal.

Additionally, the fin region of the first heat sink may have a differentvertical position than the fin region of the second heat sink. In someembodiments, the heat pipes of the given heat sink include a verticalportion and bends so that the first heat sink and the second heat sinkare interdigitated in pedestal regions, ramp regions and fin regions ofthe first heat sink and the second heat sink.

Another embodiment provides a system that includes the chip package.

Another embodiment provides a method for cooling the first integratedcircuit and the second integrated circuit during operation of the firstintegrated circuit and the second integrated circuit. During the method,heat is conducted away from the first integrated circuit using the firstheat sink mechanically coupled to the first integrated circuit.Moreover, heat is conducted away from the second integrated circuitusing the second heat sink mechanically coupled to the second integratedcircuit, where the first integrated circuit is adjacent to the secondintegrated circuit. Furthermore, the given heat sink for the givenintegrated circuit includes: the pedestal region mechanically coupled tothe given integrated circuit; the ramp region that extends the verticalposition of the portion of the given heat sink; and the fin regionhaving the fins that convectively transfer the heat to the externalfluid. Additionally, the heat pipes in the fin region of the first heatsink are interdigitated with the heat pipes in the fin region of thesecond heat sink.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram illustrating a top view of integrated circuitshaving an in-line configuration in a chip package in accordance with anembodiment of the present disclosure.

FIG. 2 is a block diagram illustrating a top view of interdigitated heatpipes in heat sinks in the chip package of FIG. 1 in accordance with anembodiment of the present disclosure.

FIG. 3 is a block diagram illustrating a side view of the interdigitatedheat pipes in the heat sinks of FIG. 1 in accordance with an embodimentof the present disclosure.

FIG. 4 is a block diagram illustrating a top view of fins in fin regionsof the heat sinks of FIG. 1 in accordance with an embodiment of thepresent disclosure.

FIG. 5 is a block diagram illustrating a top view of integrated circuitshaving a lateral configuration in a chip package in accordance with anembodiment of the present disclosure.

FIG. 6 is a block diagram illustrating a side view of interdigitatedheat pipes in the heat sinks in the chip package of FIG. 5 as a functionof integrated-circuit separation in accordance with an embodiment of thepresent disclosure.

FIG. 7 is a block diagram illustrating a top view of interdigitated heatpipes in heat sinks in the chip package of FIG. 5 in accordance with anembodiment of the present disclosure.

FIG. 8 is a block diagram illustrating a side view of interdigitatedheat pipes in pedestal regions in the heat sinks of FIG. 5 in accordancewith an embodiment of the present disclosure.

FIG. 9 is a block diagram illustrating a side view of interdigitatedheat pipes in the pedestal regions in the heat sinks of FIG. 5 inaccordance with an embodiment of the present disclosure.

FIG. 10 is a block diagram illustrating a side view of interdigitatedheat pipes in the pedestal regions in the heat sinks of FIG. 5 inaccordance with an embodiment of the present disclosure.

FIG. 11 is a block diagram illustrating a side view of a chip package inaccordance with an embodiment of the present disclosure.

FIG. 12 is a block diagram illustrating a side view of a pedestal regionof one of the heat sinks of FIG. 5 and an associated pedestal inaccordance with an embodiment of the present disclosure.

FIG. 13 is a block diagram illustrating a top view of fins in finregions of the heat sinks of FIG. 5 in accordance with an embodiment ofthe present disclosure.

FIG. 14 is a block diagram illustrating a top view of fins in finregions of the heat sinks of FIG. 5 in accordance with an embodiment ofthe present disclosure.

FIG. 15A is a block diagram illustrating a side view of heat pipes inheat sinks having different elevations in accordance with an embodimentof the present disclosure.

FIG. 15B is a block diagram illustrating a side view of heat pipes inheat sinks having different elevations in accordance with an embodimentof the present disclosure.

FIG. 16 is a block diagram illustrating a side view of a winged heatsink in accordance with an embodiment of the present disclosure.

FIG. 17 is a block diagram illustrating a top view of a winged heat sinkin accordance with an embodiment of the present disclosure.

FIG. 18 is a block diagram illustrating a three-dimensionally curvedheat pipes in heat sinks in accordance with an embodiment of the presentdisclosure.

FIG. 19 is a block diagram illustrating a system that includes a chippackage in accordance with an embodiment of the present disclosure.

FIG. 20 is a flow diagram illustrating a method for cooling a firstintegrated circuit and a second integrated circuit during operation ofthe first integrated circuit and the second integrated circuit inaccordance with an embodiment of the present disclosure.

FIG. 21 is a flow diagram illustrating a method for cooling anintegrated circuit using a heat sink in accordance with an embodiment ofthe present disclosure.

Note that like reference numerals refer to corresponding partsthroughout the drawings. Moreover, multiple instances of the same partare designated by a common prefix separated from an instance number by adash.

DETAILED DESCRIPTION

Embodiments of a chip package, a system that includes the chip package,and a technique for cooling a first integrated circuit and a secondintegrated circuit are described. This chip package includes adjacentintegrated circuits on a circuit board, and separate heat sinks arethermally coupled to the integrated circuits. Because the integratedcircuits are in close proximity, the heat pipes in the separate heatsinks are interdigitated to prevent mechanical interference between theheat sinks. The amount of interdigitation depends on the separationbetween the integrated circuits and how the integrated circuits arearranged relative to an external fluid (such as flowing air). At theminimum, the heat pipes in fin regions of the heat sinks (which includefins for convective heat transfer to the external fluid) areinterdigitated. However, the heat pipes may be interdigitated inpedestal regions of the heat sinks (which are thermally coupled to theintegrated circuits) and/or in ramp regions of the heat sinks (in whichvertical positions of the heat sinks change from the pedestal regions tothe fin regions).

By interdigitating at least portions of the heat pipes of the heatsinks, this thermal-management technique may facilitate improved thermalperformance of the heat sinks. Consequently, the thermal-managementtechnique may facilitate chip packages with multiple integrated circuitsin close proximity.

We now describe the chip package. Thermal management during operation ofintegrated circuits is often based on heat sinks that include heatpipes. The very high effective thermal conductivity of a heat pipeenhances the transport of heat over the length of the heat pipe, from aregion of the heat pipe in contact with an integrated circuit toconvective fins. In particular, the heat pipe may include awall-and-wick structure. During operation, there is an open volume forvapor transport of a heated gas, and there is a counterflow of a cooledliquid in the wick structure.

The interdigitation of heat pipes in heat sinks for adjacent orproximate integrated circuits is a function of the configuration of theintegrated circuits. FIG. 1 presents a block diagram illustrating a topview of integrated circuits 110 having an in-line configuration in achip package 100. In the in-line configuration, an external fluid (suchas air) has a flow direction 112, and integrated circuit 110-1 andintegrated circuit 110-2 are arranged adjacent to each other on circuitboard 114 along flow direction 112.

FIG. 2 presents a block diagram illustrating a top view ofinterdigitated heat pipes 212 and 216 in heat sinks 210 and 214 in chippackage 100, and FIG. 3 presents a block diagram illustrating a sideview of chip package 100. In particular, heat sink 210 includes heatpipes 212 that conduct heat away from integrated circuit 110-1 duringoperation of integrated circuit 110-1; and heat sink 214 includes heatpipes 216 that conduct heat away from integrated circuit 110-2 duringoperation of integrated circuit 110-2. A given heat sink for a givenintegrated circuit includes: a pedestal region (such as pedestal regions218) mechanically coupled to the given integrated circuit; a ramp region(such as ramp regions 220) that extends a vertical position of a portionof the given heat sink; and a fin region (such as fin regions 222)having fins that convectively transfer the heat to the external fluid(such as the air). (Note that the fins in fin regions 222 may extendover a full width of circuit board 114.) Furthermore, heat pipes 212 inthe fin region of heat sink 210 are interdigitated with heat pipes 216in the fin region of heat sink 214.

Note that the pedestal of the given heat sink in the pedestal region(such as pedestal 310 in FIG. 3) is typically copper, aluminum oranother metal alloy. (Similarly, the fins may be copper, aluminum oranother material.) The heat pipes in the pedestal region are oftenflattened to provide good contact and, thus, to improve the thermalimpedance with the top surface of the given integrated circuit.Moreover, the pedestal is typically thermally coupled to the givenintegrated circuit by a thermal-interface material (TIM) 312, such as:indium foil, carbon sheet, metal particulate impregnated grease, thermalgrease, etc. Note that the heat pipes may be thermally coupled to theheat-sink base using a low-melting-point solder.

Furthermore, note that ramp regions 220 often include simple ‘s-bends.’In particular, ramp regions 220 of heat sinks 210 and 214 curve upwardsat different distances from integrated circuits 110 so they do notmechanically interfere with each other. Note that heat sinks 210 and 214are self-aligning with the top surface of the integrated-circuitpackages. In this way, chip package 100 may address challenges such asnon-coplanar top surfaces of integrated circuits 110. In particular, thechip package may be compliant to non-coplanar die surfaces, because thetwo heatsinks permit each heatsink to make good thermal contact to itsrespective die while sharing the heatsink volume.

In general, interdigitation of heat pipes 212 and 216 in heat sinks 210and 214 is easier for the in-line configuration of integrated circuits110 than for a lateral configuration (which is described further belowwith reference to FIG. 5). In particular, note that only the portions ofheat pipes 212 and 216 in fin regions 222 are interdigitated in FIG. 2,while the portions in the ramp regions 220 are merely nested.

The heat pipes for use when the integrated circuits have the in-lineconfiguration may be assembled using the following assembly technique.Heat sink 210 (which has a shallower slope in the ramp region) ispositioned on top of integrated circuit 110-1 with a thermal-interfacematerial between them. Then, a clamping fixture for heat sink 210 isadjusted to a specified force.

Next, heat sink 214 (which has a steeper slope in the ramp region) ispositioned on top of integrated circuit 110-2 with a thermal-interfacematerial between them. Then, a clamping fixture for heat sink 214 isadjusted to a specified force.

Note that the assembly technique may involve a downward verticaltranslation of the heat sink 214 to its final position. While finregions 222 of heat sinks 210 and 214 are interdigitated, the rampregion of heat sink 214 is nested within the ramp region of heat sink210. This approach may allow flexibility in the design of the fins.

FIG. 4 presents a block diagram illustrating a top view of fins 400 infin regions 222 of heat sinks 210 and 214 in FIG. 2. Note that the finsin the fin region of heat sink 210 and the fins in the fin region ofheat sink 214 may be: aligned, staggered and/or overlapped (orextended). Note that ‘staggered fins’ may overlap between the heatpipesso that they almost touch the heatpipes to which they are not connected;while the ‘scalloped extended fins’ extend even further, so that theheatpipes fit with a little bit of clearance into the scallops of thefins which are attached to the other heatpipes. The use of so-called‘singulated’ fins may allow the use of tall or longer fins in a verticaldirection. In other embodiments, however, scalloped, extended fins areused. These extended fins may provide more area and greater stabilitythan singulated fins. In some embodiments, the heat-pipe regions of theheat sinks have different elevations or heights. This may allow the useof a configuration in which the fins from the two heat sinks areinterleaved vertically (with one set pointing downward and another setpointed upward).

We now describe heat sinks for use in the lateral configuration of theintegrated circuits. FIG. 5 presents a block diagram illustrating a topview of integrated circuits 110 having a lateral configuration in a chippackage 500. In particular, integrated circuit 110-1 and integratedcircuit 110-2 are arranged perpendicular to flow direction 112 with anintegrated-circuit separation 510.

The lateral configuration poses several design challenges. Notably, theheat pipes from one heat sink may overhang the pedestal region of aneighboring heat sink. Consequently, the ramp regions of the two heatsinks cannot be simply nested. For close integrated-circuit separations,the heat pipes in the ramp regions may also have to be interdigitated.Furthermore, in general the assembly technique used for the in-lineconfiguration (which was described previously) may not be applicable tothe lateral configuration.

FIG. 6 presents a block diagram illustrating a side view ofinterdigitation of heat pipes 612 and 616 in heat sinks 610 and 614 inchip package 500 (FIG. 5) as a function of integrated-circuit separation618. Heat pipes 612 of heat sink 610 in at least a portion of rampregion 622-1 of heat sink 610 are interdigitated with heat pipes 616 ofheat sink 614 in at least a portion of ramp region 622-2 of heat sink614. Furthermore, heat pipes 612 of heat sink 610 in at least a portionof pedestal region 620-1 of heat sink 610 may be interdigitated withheat pipes 616 of heat sink 614 in at least a portion of pedestal region620-2 of heat sink 614. Thus, heat sinks 610 and 614 may beinterdigitated in ramp regions 622 and fin regions 624 or in pedestalregions 620, ramp regions 622 and fin regions 624. For clarity, notethat the fins are not shown in FIG. 6.

In general, the degree of interdigitation depends on theintegrated-circuit separation and a height difference between the top ofthe pedestals and the lower edge of an interdigitated zone of rampregions 622. For example, if the integrated-circuit separation or thelateral spacing is large enough, heat pipes 612 and 616 may only beinterdigitated in fin regions 624. As the lateral spacing is reduced,heat pipes 612 and 616 may be interdigitated at the top of ramp regions622. Furthermore, with further reduction in the lateral spacing, heatpipes 612 and 616 may be interdigitated at the bottom of ramp regions622. Additionally, with even further reduction in the lateral spacing,heat pipes 612 and 616 may be interdigitated in pedestal regions 620.Consequently, the closest lateral spacings may result in interdigitationover most of the lengths of heat pipes 612 and 616.

FIG. 7 presents a block diagram illustrating a top view ofinterdigitated heat pipes 612 and 616 in heat sinks 610 and 614 (FIG. 6)in chip package 500.

The ability to interdigitate heat pipes from one heat sink with those ofanother in the ramp regions and the pedestal regions also depends on theheat-pipe separation at the precise value of the lateral separation. Ingeneral, the separation between the heat pipes depends on: the heightdifference, the heat-pipe pitch in the pedestal region, the heat-pipepitch in the fin region, the fan-out angle and the heat-pipe thicknessat a particular location. For interdigitation to be possible, theseparation of the heat pipes usually must be greater than the heat-pipethickness at each heat-pipe location.

A variety of designs may be used in the pedestal region to facilitateinterdigitation of heat pipes in heat sinks. FIG. 8 presents a blockdiagram illustrating a side view of interdigitated heat pipes 812 and814 in the pedestal regions of heat sinks 610 and 614 (FIG. 6). In theseembodiments, heat pipes 812 in the pedestal region of heat sink 610 maybe aligned with heat pipes 814 in the pedestal region of heat sink 614.In particular, heat pipes 812 and 814 may be soldered to bottom surfacesof pedestals in the pedestal regions. Moreover, heat pipes 812 and 814in the pedestal regions may be aligned. When the pedestal is about thesame size as the integrated circuit, the heat pipes are in uniformthermal contact with the top surface of the integrated circuit. However,because heat pipes 812 and 814 terminate at the same locations in thepedestals, the minimum value of the height separation in theinterdigitated zone of the ramp regions is some distance from the top ofthe pedestals (i.e., there is a minimum possible height separation).This may limit the minimum lateral separation between the two pedestals.

FIG. 9 presents a block diagram illustrating a side view ofinterdigitated heat pipes 912 and 914 in the pedestal regions of heatsinks 610 and 614 (FIG. 6). In this example, heat pipes 912 and 914 maybe soldered to bottom surfaces of the pedestals in the pedestal regions.Moreover, heat pipes 912 in the pedestal region of heat sink 610 may bestaggered between heat pipes 914 in the pedestal region of heat sink614. In particular, the heat pipes in one pedestal may be offset by thepitch with respect to those in the other pedestal. Note that across-section of heat pipes 912 in the pedestal region of heat sink 610and a cross-section of heat pipes 914 in the pedestal region of heatsink 614 may be modified at interdigitated locations. For example, theheat pipes can be ‘squished’ at interdigitated locations to facilitate asmaller pitch.

Note that each of the pedestals may be a bit oversized with respect tothe outline of the integrated circuits because the two integratedcircuits may need to be co-linear. When heat pipes 912 and 914 in thepedestal regions are fully interdigitated, the height difference may benegative and the mechanical interference between heat pipes 912 and 914may no longer be the limiting factor controlling the separation betweenthe pedestals. Instead, the limiting factor may be the contact betweenthe heat pipes of one heat sink with the pedestal of the other.Consequently, in this case, the minimum separation may be determined bythe bending radius of the heat pipes, etc.

FIG. 10 presents a block diagram illustrating a side view ofinterdigitated heat pipes 1012 and 1014 in the pedestal regions of heatsinks 610 and 614 (FIG. 6). This example shows a so-calledzero-clearance configuration. In particular, there are bends in heatpipes 1012 and 1014, which route them vertically from the plane of thepedestals. The upper portions of heat pipes 1012 and 1014 fan outlaterally. When viewed end on, heat pipes 1012 and 1014 interdigitateover the entire length (including regions within the footprint of thepedestals), which allows the integrated-circuit separation to bereduced. In this example, heat pipes 1012 and 1014 may be soldered tomounting lands on top of copper pedestals. Note that copper is typicallyused because of its high thermal conductivity. In the pedestal regions,heat pipes 1012 and 1014 may have square cross-sections.

Using the zero-clearance configuration, heat pipes 1012 and 1014 andfins from heat sinks 610 and 614 (FIG. 6) do not contact each other evenfor zero clearance between the pedestals. As a practical matter, giventhe tolerances in manufacturing, some clearance is typically needed toprevent the pedestals from contacting because such contact wouldjeopardize their mechanical independence from each other.

In general, the chip package may include an optional lid and/or anoptional pedestal in the pedestal region of the given heat sink. This isshown in FIG. 11, which presents a block diagram illustrating a sideview of a chip package 1100. In particular, chip package 1100 includesan optional lid 1110 (which provides protection during handling of chippackage 1100). Note that optional lid 1110 may be made of copper. Inaddition, there may be a flange to clamp a given heat pipe to a givenintegrated circuit. The clamping force applied to the given heat sinkusing the flange may keep the given heat sink aligned with the givenintegrated circuit. For example, the clamping force may be applied usinga screw/spring assembly.

In particular, when there is a large integrated-circuit separation, theflanges can extend laterally beyond the integrated-circuit packagetoward the centerline with the other integrated circuit. The additionalrouting length of the heat pipes with wider flanges may enhanceheat-load balancing between different heat pipes. Alternatively, formoderate and/or close integrated-circuit separation, the extension ofthe flanges in the lateral direction may be small (particularly in thedirection of the other integrated circuit) in order to manage the moreaggressive interdigitation of the heat pipes in the ramp regions.Furthermore, on the side of the flange away from the other integratedcircuit, the tolerances for the lateral flange extension and theproximity of the heat-pipe ramp region to the edge of the flange may bemore relaxed.

In some embodiments, chip package 1100 has no lid (which is sometimesreferred to as a ‘bare-die package’). This configuration may providethermal advantages. It may also allow the pedestals to be significantlysmaller than the package substrate.

The integrated-circuit separation on a circuit board may be determinedby signal-integrity and trace-routing considerations and a need tolocate other components nearby. In general, the pedestals for a bare(lidless) die are about the same size as the die, and the pedestals fora lidded package can range from about the same size as the die to aboutthe same size as the package. Consequently, for the sameintegrated-circuit spacing, the heat-sink pedestals for cooling lidlesspackages may have a greater separation than for lidded packages. Thisimplies that a less aggressive interdigitation strategy may be neededfor a lidless package compared to a lidded one for the sameintegrated-circuit separation. Thus, there may not need to beinterdigitation in the ramp regions for a lidless package, while thismay be needed for a lidded package.

We now describe pedestal design for lidless chip packages. Integratedcircuits often have regions of high heat flux compared with the averageheat flux over the entire die. The copper lid on a lidded chip packagehelps spread out the heat from these hot spots as it flows to theheat-sink pedestals and, thus, helps reduce the peak temperatures. Inturn, this can result in more-efficient cooling and less of a chance ofexceeding the local ability of the heat pipes to remove heat.Consequently, as shown in FIG. 11, in many cases it may be necessary touse heat sinks with copper pedestals at the interfaces with theintegrated circuits, with the heat pipes attached to the top of thepedestals.

In principle, aligned or staggered heat pipes can be used in thepedestal region for lidless chip packages. For the sameintegrated-circuit separation, there is typically greater heat-sinkpedestal separation when a pedestal is used. This may reduce the chanceof mechanical interference between the heat pipes of one heat sink andthe pedestal of the neighboring heat sink for small pedestalseparations.

If the previous design approaches provide insufficient cooling of hotspots, additional techniques can be used. These techniques usuallymodify the common width of the heat pipes in the heat sinks and/or thecommon thickness of the pedestals. In particular, for the portions ofthe pedestal/heat-pipe assembly overlapping regions of the highest heatflux: the width of the flattened heat pipes may be reduced to reduce thetotal power transported by each heat pipe; and/or the local thickness ofthe pedestal may be increased to spread the heat more uniformly over theheat pipe.

This is shown in FIG. 12, which presents a block diagram illustrating aside view of a pedestal region and an associated pedestal 1212 of one ofheat sinks 610 and 614 (FIG. 6) in chip package 1200. In FIG. 12, widths1214 of at least a subset of the heat pipes of the given heat sink maybe varied over lengths of at least the subset of the heat pipes.Furthermore, a thickness of the given pedestal may be varied over awidth of the given pedestal.

We now describe assembly techniques for use with integrated circuits inthe lateral configuration. In a lateral-translation assembly technique,thermal-interface material may be applied to both integrated circuits.Then, the first heat sink may be positioned on top of the firstintegrated circuit, and the clamping fixture for the first heat sink maybe adjusted to a specified force. Next, in a downward motion, the rightfin region of the second heat sink may be interdigitated with the finregion of the first heat sink, stopping slightly above the finalelevation. Moreover, the second heat sink may be translated horizontallytoward the center of the first heat sink until the center of the secondheat sink lines up with the integrated-circuit package (while avoidingdisturbance of the thermal-interface material on the second integratedcircuit). Furthermore, the second heat-sink clamping fixture may beadjusted to a specified force.

For heat pipes with a double s-bend in the ramp regions, thelateral-translation assembly technique may require short fin lengths,which may limit the thermal-cooling efficiency. While variable finlengths may be used, this may result in a variable thermal resistanceamong the heat pipes. Alternatively, adding an additional bend to createa vertical routing path for the heat pipes (as shown in FIG. 10) mayfacilitate longer fin lengths.

In general, the lateral-translation assembly technique allows sequentialmounting of the heat sinks. This assembly technique may be used withsingulated fins having a width less than a heat-pipe pitch in the finregions.

Alternatively, in an orthogonal-insertion assembly technique, singulatedfins in heat pipes may be assembled by rotating two heat sinks togetherlike the blades in a pair of scissors. In particular, a first heat sinkmay be held in a horizontal position. Then, the second heat sink may betranslated vertically while the fin region of the second heat sinkinterdigitates with the fin region of the first heat sink. Thistranslation may stop when the ramp region of the second heat sinkreaches the fin region of the first heat sink. Next, the second heatsink may be rotated by 90° until its fin region is coplanar with that ofthe first heat sink so that the heat pipes can be interdigitated in thedesired manner. Note that the heat sinks may be kept in rough alignmentas they are lowered as a pair to each contact their respectiveintegrated circuit (with previously applied thermal-interface material).Furthermore, individual clamping fixtures of the heat sinks may besequentially adjusted to obtain a specified force.

The orthogonal-insertion assembly technique may be modified if there areextended fins in the heat sinks. In particular, the first operation inthe assembly technique may be the same except that the heat pipes of thesecond heat sink being interdigitated with those of the first heat sinkmay have no fins attached. After this operation, the fins may beattached to the heat pipes in the second heat sink. Next, the secondheat sink may be rotated by 90°, and the heat sinks may beinterdigitated in the desired manner.

In the orthogonal-insertion assembly technique, either aligned orstaggered singulated fins may be used. For scalloped, extended fins, thefins can be mounted on both wings of the first (horizontal) heat sinkand the lower wing of the second (vertical) heat sink prior toinsertion. Then, the fins can be mounted to the upper wing of the secondheat sink following insertion.

Note that the orthogonal-insertion assembly technique may allow the useof fins having a longer lower portion than the lateral-insertionassembly technique. Consequently, the orthogonal-insertion assemblytechnique may be more suitable for low-profile heat sinks than thelateral-insertion assembly technique. If the orthogonal-insertionassembly technique is used with additional bends for vertical routing,there can be zero clearance between pedestals. However, the heat sinkstypically need to be interdigitated first and then mounted as a looselycoupled pair. This assembly technique works with staggered fins having awidth greater than a heat-pipe pitch in the fin region. In someembodiments, the fins are curved for use with the orthogonal-insertionassembly technique.

For either assembly technique, in air-flow regions where only one heatsink has fins, it may be necessary to have a locally reduced fin pitchto maintain a uniform flow impedance (in particular, in order tominimize bypass flow). Alternatively, it may be necessary to attach alocal baffle to block the bypass flow. In some embodiments, the finpitch of a heat sink in locally reduced (relative to the pitch of thefins in the remainder of the heat sink) in a region directly above thepedestal of the other heat sink. This configuration may result in auniform fin pitch to air flow when two such heat sinks areinterdigitated because the interdigitated fins in the remainders of theheat sink may match that in the region with the locally reduced pitch(where the fins are not interdigitated).

In some embodiments, there may be heat-transfer advantages (such as lessobstructed airflow) if the heat sinks have different vertical heights.In these configurations, the heat pipes can even serve to channel flowinto a region at a height range bounded by the two rows of heat pipes.As described further below, in these embodiments enhanced fin structuresare possible in which there is a wider strip of continuous metal fromthe leading edge to the trailing edge.

FIG. 13 presents a block diagram illustrating a top view of fins 1300 inthe fin regions of heat sinks 610 and 614 (FIG. 6). Note that the finsin the fin region of heat sink 610 and the fins in the fin region ofheat sink 614 may be: aligned, staggered and/or overlapped. Once again,note that ‘staggered fins’may overlap between the heatpipes so that theyalmost touch the heatpipes to which they are not connected; while the‘scalloped extended fins’ extend even further, so that the heatpipes fitwith a little bit of clearance into the scallops of the fins which areattached to the other heatpipes. In addition, as discussed previously,scalloped extended fins or enhanced extended fins may be used. Ingeneral, a variety of fin shapes (which may just barely clear boardcomponents of multiple heights) may be used (e.g., with an upside-downor baseless heatsink).

As described below with reference to FIGS. 15A and 15B, in someembodiments the heat sinks have different vertical heights orelevations. This may allow the use of different types of scallopedextended fins. FIG. 14 presents a block diagram illustrating a top viewof fins 1400 in the fin regions of heat sinks 610 and 614 (FIG. 6). Notethat the fins in the fin region of heat sink 610 and the fins in the finregion of heat sink 614 may be overlapped. In this example, a fin-downbase may be soldered to an upper heat pipe and fin-up base may besoldered to a lower heat pipe. Moreover, the fins in heat sinks 610 and614 may be interleaved. This configuration allows use of parallel platefins for improved efficiency and a uniform fin width from the leadingedge to the trailing edge.

FIG. 15A, which presents a block diagram illustrating a side view ofheat pipes 1512 and 1514 in chip package 1500 having differentelevations 1518 in heat sinks 1510 and 1516. In particular, the finregion of heat sink 1510 may have a different vertical position than thefin region of heat sink 1516. Note that the given heat sink may includeheat pipes having a vertical portion and bends so that heat sink 1510and heat sink 1516 are interdigitated in the pedestal regions, the rampregions and the fin regions of heat sinks 1510 and 1516.

Moreover, heat pipes 1512 and 1514 may or may not be interdigitated inFIG. 15A. For example, in embodiments where they are not interdigitated,the lower half of the heat pipes may be attached to the upstreampedestal and the upper half of the heat pipes may be attached to thedownstream, pedestal.

During assembly of the configuration shown in FIG. 15A with the in-lineconfiguration of the integrated circuits, heat sink 1510 with the lowerfin-region heat pipes may be mounted first. Because the direction ofmovement of heat pipes 1514 may be directed downward during assembly,heat sink 1510 may have a lower fin region on both wings. Conversely,heat sink 1516 may have an upper fin region on both wings.

FIG. 15B presents a block diagram illustrating a side view of heat pipes1512 and 1514 in chip package 1550 having different elevations 1518 inheat sinks 1510 and 1516 for a lateral configuration. Note that heatpipes 1512 and 1514 may not be interdigitated in this configuration.

In some embodiments, a base assembly with integral fins is soldered toflattened heat pipes in the fin region to achieve a design with asingle-elevation heat-pipe region. In particular, each of the heat sinksmay have a fin structure in which the fins are soldered to one side of aplate. The other side of the plate is then soldered to flattened heatpipes of only one of the heat sinks in the fin region. Thus, each heatsink may be assembled from two pieces. Each of the pieces may haveflattened heat pipes arranged on a surface. These heat pipes may beinterdigitated parallel to each other when the two pieces are solderedtogether (so that the surfaces of the two pieces are parallel to eachother and face each other with the fins from each of the two platesextending in opposite directions), thereby implementing the heat sink.Care is taken during the soldering operation to ensure that the platefor a given heat sink is not soldered to the heat pipes of the otherheat sink. This is to maintain the mechanical independence of the twoheat sinks.

The thermal-management technique may be applied to cooling larger arraysof integrated circuits, such as a 2×2 or N×M (where N and M areintegers) array of integrated circuits. This may involve the assembly oftwo heat-sink pairs. Each of the heat-sink pairs may have a lateralconfiguration of two heat sinks with interdigitated heat pipes. Thefirst heat-sink pair may have a ramp region extending farther out thanthe ramp region of the second heat-sink pair. This may allow the firstheat-sink pair and the second heat-sink pair to be nested (as describedpreviously for the in-line configuration). If desired, the embodimentsand techniques described previously can be used to enable near contactbetween the pedestals of the four individual heat sinks.

In some embodiments, the heat sinks have curved fins to provide properclearance between the fins of the two heat sinks to facilitate anorthogonal-insertion assembly technique when the fin pitch is verysmall. Moreover, the flange may be designed to enable interdigitation ofheat pipes at various pedestal separations. In addition, mechanicalindependence of the interdigitated heat sinks may constrain the geometryof the heat pipes.

The preceding embodiments of the thermal-management technique with heatsinks having interdigitated heat pipes may be used separately from or inconjunction with embodiments of a winged heat sink. The winged heat sinkuses sets of heat pipes to create an effective thermal path and thermaldistribution from a thermal load (such as an integrated circuit) to heatdissipation or convective fins located at a high airflow area, whilemaximizing available board area and available headroom for componentsnear the thermal load, such as voltage-regulator modules (however,voltage-regulator modules are often tall devices that can restrict airflow and present height issues, notably when the height of thevoltage-regulator modules nears or exceeds the height of the processor).

In particular, the winged heat sink may maximize the elevation of thethermal path associated with the winged heat sink above a circuit board(particularly near the processor) so that fin orientation of the wingedheat sink can be inverted, thereby allowing taller components and othercomponents to be placed nearby. For example, downward facing fins on thewinged heat sink may match the topologies of components on an underlyingcircuit board. The winged heat sink may also maximize the flexibility ofthe thermal path to place the thermal load in maximally effectiveairflows, and may increase potential cooling fin cross-sections anddepth in the maximally effective airflows. In particular, the heat pipesmay be routed to any region of the system where the heat flow isgreatest. In addition, the winged heat sink may minimize parts andproduction costs.

These improvements associated with the winged heat sink may be afunction of using thermal transfer devices to move the heat load and achanged focus from uniform heat rejection fins to maximizing the use ofheat rejection fins principally in the area of highest airflow. In thediscussion that follows, heat sinks with heat pipes are used asillustrations of the thermal transfer device. However, in otherembodiments the winged heat sink may be used with other thermal transferdevices (including those that exclude heat pipes).

FIG. 16 presents a block diagram illustrating a side view of a wingedheat sink 1600. In this winged heat sink, one or more heat pipes 1618transfer heat from an optional pedestal 1614 (which is thermally coupledto integrated circuit 1610, for example, by thermal-interface material1608) to fins 1620. (Thus, winged heat sink 1600 may have one or morearms 1616. Embodiments with one arm may be used when there is singlesource of cooling air flow.) Note that fins 1620 may be optimized insize, orientation and attachment to an optional pedestal 1614.Furthermore, fins 1620 may be directly attached to one or more arms 1616to provide a reduced-cost, high-thermal efficiency configuration. Inaddition, fins 1620 may spread the thermal load to provide a larger finlength in the direction of the air flow(s). This spreading of thethermal load may be asymmetric in multiple dimensions.

Moreover, the one or more heat pipes 1618 extends height 1622 of wingedheat sink 1600 along vertical direction 1624. Furthermore, note thatfins 1620 are facing downward toward circuit board 1612 on whichintegrated circuit 1610 is mounted (i.e., toward plane 1626 ofintegrated circuit 1610 and/or pedestal 1614). In this way, winged heatsink 1600 may match a topology (defined by other components) of circuitboard 1612 in proximity to integrated circuit 1610.

In some embodiments, winged heat sink 1600 includes optionalupward-facing fins 1628 and/or optional fins 1630 along sides of wingedheat sink 1600.

Moreover, fins 1620 may have variable lengths (such as length 1632)along the one or more heat pipes 1618 and/or in a direction into theplane of FIG. 16. Thus, variable lengths may be along one dimension ortwo dimensions of winged heat sink 1600. This may provide additionaldegrees of freedom to accommodate the topology of the other componentsand, more generally, circuit board 1612. For example, thevariable-length fins may provide clearances or notches to clearcomponents and optimize cooling efficiency and effectiveness.

Note that winged heat sink 1600 may include an optional copper plate(such as a heat-sink base) or an optional heat-sink base 1634. In someembodiments, heat-sink base 1634 is cooled using a pumped liquid thatflows through it. This optional heat-sink base may spread thetransported heat so the liquid in the one or more heat pipes 1618 doesnot dry up. Moreover, optional heat-sink base 1634 may be located aboveor below the one or more heat pipes 1618 at pedestal 1614. Moregenerally, optional heat-sink base 1634 may be located along some or allof the length of the one or more heat pipes 1618, and may be locatedabove, below or around the one or more heat pipes 1618. Furthermore,optional heat-sink base 1634 may be distributed asymmetrically aroundwinged heat sink 1600.

As shown in FIG. 17, which presents a block diagram illustrating a topview of a winged heat sink 1600, the winged heat sink may includemultiple (quasi-parallel) arms 1616. This may facilitate heat transportalong directions 1710 and/or 1712, which may allow more surface area forfins in regions of circuit board 1612 where there are no or fewercomponents.

The winged heat sink may allow large components (such as avoltage-regulator module and/or other integrated circuits) to be placednear integrated circuit 1610 by vertically clearing the adjacentcircuit-board area, and/or may improve the thermal-fin area in theeffective cooling air flows (which may be relevant in the case where theair flows do not pass over integrated circuit 1610). Thus, the wingedheat sink may: improve the thermal path through component elimination,lower the weight of the heat sink (which may reduce the effects of shockand vibration), and reduce cost by eliminating parts in the heat sink.

In an exemplary embodiment, the winged heat sink is used in blade-typeserver system designs in which electrical connectors occupy the spaceotherwise preferred for cooling air flows. However, the winged heat sinkmay be used in other applications of computer design, power conversionsand other industries where high-powered components are cooled.

In some embodiments, the heat pipes in the heat sinks may be curved inthree dimensions. This is shown in FIG. 18, which presents a blockdiagram illustrating a three-dimensionally curved heat pipes 1812 inheat sinks 1810 of chip package 1800. For clarity, note that the finsare not shown in FIG. 18. By curving heat pipes 1812, athree-dimensional weave may be created, allowing heat sinks 1810 tocurve up or down, or to cross each other in and around integratedcircuits 110. In particular, the heat pipes are attached to one of thepedestals. Hence, these heat pipes are not interdigitated. Instead, eachbunch of adjacent heat pipes reciprocally swerves around the otherbunch. Moreover, each of the dies are covered by heat pipes 1812. Notethat, at the heatpipe inflection plane, all of heatpipes 1812 are at thesame height. Furthermore, at the heatpipe convergence plane, half theheatpipes are at the die surface level, while the other half are at themaximum height. Additionally, the height is ramped from die surface totop between the two convergence planes. In some embodiments, a staggeredor flattened configuration of the heat pipes is used for improvedperformance and/or one or more heatpipes are shared.

This embodiment, as well as those illustrated in FIGS. 16 and 17, mayallow the heat pipes to be routed to any region of a system where theheat flow is greatest (in doing so, they would naturally avoid anyobstacles in their routing.) In FIG. 18, each heat sink is,reciprocally, an obstacle to the other. These obstacles can be avoidedby having the heat pipes of each heat sink reciprocally swerve aroundthose of the other heat sink.

Embodiments of the chip package and/or the winged heat sink may be usedin a wide variety of applications, such as: a die stack in a memoryapplication, flip-chip bonding and/or multi-layer stacks. A generalapplication of a system (such as an electronic device) is shown in FIG.19, which presents a block diagram illustrating a system 1900. Thissystem includes chip package 1910, which may include one or more of thechip packages in the preceding embodiments (including those with theheat sinks having interdigitated heat pipes and/or the winged heatsink).

Chip package 1910 may include: VLSI circuits, communication systems(such as in wavelength division multiplexing), storage area networks,data centers, networks (such as local area networks), and/or computersystems (such as multiple processor-core computer systems). For example,a chip package may be included in a backplane that is coupled tomultiple processor blades, or a chip package may couple different typesof components (such as processors, memory, I/O devices, and/orperipheral devices). In some embodiments, a chip package performs thefunctions of: a switch, a hub, a bridge, and/or a router.

Note that system 1900 may include, but is not limited to: a server, alaptop computer, a communication device or system, a personal computer,a work station, a mainframe computer, a blade, an enterprise computer, adata center, a portable-computing device, a tablet computer, asupercomputer, a network-attached-storage (NAS) system, astorage-area-network (SAN) system, and/or another electronic computingdevice. Moreover, note that a given computer or computer system may beat one location or may be distributed over multiple, geographicallydispersed locations.

The embodiments of the chip package, the winged heat sink and/or thesystem may include fewer components or additional components. Forexample, there may be more than two interdigitated heat sinks in thechip package. Furthermore, although the chip package, the winged heatsink and the system in the preceding discussion are illustrated ashaving a number of discrete items, these embodiments are intended to befunctional descriptions of the various features that may be presentrather than structural schematics. Consequently, in these embodimentstwo or more components may be combined into a single component, and/or aposition of one or more components may be changed.

Note that the circuit board in the preceding embodiments may include: asemiconductor (such as silicon or a silicon-on-insulator wafer), anorganic material, a ceramic, glass, and/or a plastic.

We now describe embodiments of the method. FIG. 20 presents a flowdiagram illustrating a method 2000 for cooling a first integratedcircuit and a second integrated circuit during operation of the firstintegrated circuit and the second integrated circuit, which may beperformed using one of the embodiments of heat sinks havinginterdigitated heat pipes. During the method, heat is conducted awayfrom the first integrated circuit using a first heat sink mechanicallycoupled to the first integrated circuit (operation 2010). Moreover, heatis conducted away from the second integrated circuit using a second heatsink mechanically coupled to the second integrated circuit (operation2012), where the first integrated circuit is adjacent to the secondintegrated circuit. Furthermore, a given heat sink for a givenintegrated circuit includes: a pedestal region mechanically coupled tothe given integrated circuit; a ramp region that extends a verticalposition of the portion of the given heat sink; and a fin region havingfins that convectively transfer the heat to an external fluid.Additionally, first heat pipes in the fin region of the first heat sinkare interdigitated with second heat pipes in the fin region of thesecond heat sink.

FIG. 21 presents a flow diagram illustrating a method 2100 for coolingan integrated circuit using a heat sink, which may be performed usingone of the embodiments of the winged heat sink. During the method, heatis transported from the integrated circuit to convective fins using anarm in the heat sink (operation 2110), where the arm extends a verticalposition of the heat sink from a plane of the integrated circuit to asecond vertical position, which is further away from the integratedcircuit. Then, the convective fins are convectively cooled, where theconvective fins extend downward from the arm back towards the integratedcircuit (operation 2114).

In some embodiments, during the transport (operation 2110), the heat isoptionally spread over the heat sink using a heat-sink base in the heatsink (operation 2112).

Moreover, in some embodiments the heat is optionally transported fromthe integrated circuit to additional convective fins using the arm(operation 2116). For example, the additional convective fins may extendupward away from the integrated circuit and/or may extend approximatelyparallel to a plane of the integrated circuit. Then, the additionalconvective fins are optionally convectively cooled (operation 2118).

In some embodiments, methods 2000 (FIG. 20) and/or 2100 includeadditional or fewer operations. Moreover, the order of the operationsmay be changed, and/or two or more operations may be combined into asingle operation.

In the preceding description, we refer to ‘some embodiments.’ Note that‘some embodiments’ describes a subset of all of the possibleembodiments, but does not always specify the same subset of embodiments.

The foregoing description is intended to enable any person skilled inthe art to make and use the disclosure, and is provided in the contextof a particular application and its requirements. Moreover, theforegoing descriptions of embodiments of the present disclosure havebeen presented for purposes of illustration and description only. Theyare not intended to be exhaustive or to limit the present disclosure tothe forms disclosed. Accordingly, many modifications and variations willbe apparent to practitioners skilled in the art, and the generalprinciples defined herein may be applied to other embodiments andapplications without departing from the spirit and scope of the presentdisclosure. Additionally, the discussion of the preceding embodiments isnot intended to limit the present disclosure. Thus, the presentdisclosure is not intended to be limited to the embodiments shown, butis to be accorded the widest scope consistent with the principles andfeatures disclosed herein.

What is claimed is:
 1. A chip package, comprising: a circuit board; afirst integrated circuit and a second integrated circuit disposed on thecircuit board, wherein the first integrated circuit is adjacent to thesecond integrated circuit; a first heat sink having a first set of heatpipes, wherein the first set of heat pipes conducts heat away from thefirst integrated circuit; and a second heat sink having a second set ofheat pipes, wherein the second set of heat pipes conducts heat away fromthe second integrated circuit; wherein each heat sink for eachintegrated circuit includes: a pedestal region comprising a pedestalmechanically coupled to the integrated circuit, wherein each heat pipein the pedestal region of the heat sink is attached to the pedestal; aramp region comprising a ramp for each heat pipe in the heat sink,wherein the ramp for each heat pipe extends a vertical position of aportion of the given heat sink; and a fin region having fins, whereinthe fins convectively transfer the heat to an external fluid; andwherein the first set of heat pipes in the fin region of the first heatsink are interdigitated with the second set of heat pipes in the finregion of the second heat sink.
 2. The chip package of claim 1, whereinthe fins in the fin region of the first heat sink and the fins in thefin region of the second heat sink are one of: aligned, staggered andoverlapped.
 3. The chip package of claim 1, wherein the external fluidhas a flow direction; and wherein the first integrated circuit and thesecond integrated circuit are arranged along the flow direction.
 4. Thechip package of claim 1, wherein the chip package further includes alid.
 5. The chip package of claim 1, wherein the external fluid has aflow direction; wherein the first integrated circuit and the secondintegrated circuit are arranged perpendicular to the flow direction; andwherein the first set of heat pipes in at least a portion of the rampregion of the first heat sink are interdigitated with the second set ofheat pipes in at least a portion of the ramp region of the second heatsink.
 6. The chip package of claim 5, wherein the first set of heatpipes in at least a portion of the pedestal region of the first heatsink are interdigitated with the second set of heat pipes in at least aportion of the pedestal region of the second heat sink.
 7. The chippackage of claim 5, wherein the first set of heat pipes in the pedestalregion of the first heat sink are aligned with the second set of heatpipes in the pedestal region of the second heat sink.
 8. The chippackage of claim 5, wherein the first set of heat pipes in the pedestalregion of the first heat sink are staggered between the second set ofheat pipes in the pedestal region of the second heat sink.
 9. The chippackage of claim 5, wherein a cross-section of the first set of heatpipes in the pedestal region of the first heat sink and a cross-sectionof the second set of heat pipes in the pedestal region of the secondheat sink are modified at interdigitated locations.
 10. The chip packageof claim 5, wherein the chip package further includes a lid.
 11. Thechip package of claim 10, wherein a width of at least a subset of thepipes of the first heat sink is varied over lengths of at least thesubset of the heat pipes.
 12. The chip package of claim 10, wherein athickness of the pedestal is varied over a width of the pedestal. 13.The chip package of claim 5, wherein the fin region of the first heatsink has a different vertical position than the fin region of the secondheat sink.
 14. The chip package of claim 5, wherein the heat pipes ineach heat sink include a vertical portion and bends so that the firstheat sink and the second heat sink are interdigitated in pedestalregions, ramp regions and fin regions of the first heat sink and thesecond heat sink.
 15. A system, comprising a chip package, wherein thechip package includes: a circuit board; a first integrated circuit and asecond integrated circuit disposed on the circuit board, wherein thefirst integrated circuit is adjacent to the second integrated circuit; afirst heat sink having a first set of heat pipes, wherein the first setof heat pipes conducts heat away from the first integrated circuit; anda second heat sink having a second set of heat pipes, wherein the secondset of heat pipes conducts heat away from the second integrated circuit;wherein each heat sink for each integrated circuit includes: a pedestalregion comprising a pedestal mechanically coupled to the integratedcircuit, wherein each heat pipe in the pedestal region of the heat sinkis attached to the pedestal; a ramp region comprising a ramp for eachheat pipe in the heat sink, wherein the ramp for each heat pipe extendsa vertical position of a portion of the heat sink; and a fin regionhaving fins, wherein the fins convectively transfer the heat to anexternal fluid; and wherein the first set of heat pipes in the finregion of the first heat sink are interdigitated with the second set ofheat pipes in the fin region of the second heat sink.
 16. The system ofclaim 15, wherein the external fluid has a flow direction; and whereinthe first integrated circuit and the second integrated circuit arearranged along the flow direction.
 17. The system of claim 15, whereinthe external fluid has a flow direction; wherein the first integratedcircuit and the second integrated circuit are arranged perpendicular tothe flow direction; and wherein the first set of heat pipes in at leasta portion of the ramp region of the first heat sink are interdigitatedwith the second set of heat pipes in at least a portion of the rampregion of the second heat sink.
 18. A method for cooling a firstintegrated circuit and a second integrated circuit during operation ofthe first integrated circuit and the second integrated circuit, whereinthe method comprises: conducting heat away from the first integratedcircuit using a first heat sink mechanically coupled to the firstintegrated circuit; and conducting heat away from the second integratedcircuit using a second heat sink mechanically coupled to the secondintegrated circuit, wherein the first integrated circuit is adjacent tothe second integrated circuit; wherein each heat sink for eachintegrated circuit includes: a pedestal region comprising a pedestalmechanically coupled to the integrated circuit, wherein each heat pipein the pedestal region of the heat sink is attached to the pedestal; aramp region comprising a ramp for each heat pipe in the heat sink,wherein the ramp for each heat pipe extends a vertical position of aportion of the heat sink; and a fin region having fins, wherein the finsconvectively transfer the heat to an external fluid; and wherein a firstset of heat pipes in the fin region of the first heat sink areinterdigitated with a second set of heat pipes in the fin region of thesecond heat sink.